- From: Jean-Claude Dufourd <jean-claude.dufourd@enst.fr>
- Date: Wed, 19 Feb 2003 20:54:29 +0100
- To: public-tt@w3.org
Dear all, Going back to a conceptual level, John Birch's requirements are: 1- a movie constituted of a video stream and an audio stream and a subtitles stream (actually, possibly many audio and subtitles), should be playable in sync, whatever part is played in whatever sequence 2- a movie should be playable according to an edit list 1 seems a TT requirement, whereas 2 does not. 2 is more of a requirement on the player. Right ? If that is so, then considering 1, I prefer putting the synchronization in a file defining the composition of streams, rather than having it specified in the subtitles stream. So I'd vote for the SMIL2.0-like solution (with adjusted/clarified semantics if needed) Now, just a word about playing a movie according to an edit list. I question the relevance of requirement 2. Given that all videos encodings I know use I (key or intra-coded) frames and non-I (frames you cannot start decoding at, you have to go back to the previous I frame), I have doubts about the feasibility, with current machines, of playing a stream according to an edit list that is not aligned with I frames. Since cuts would statistically not be aligned with I frames, a new cut set would require partial reencoding of the video. So the automatic adjustment of the subtitles stream seems reasonable. The same adjustment may be needed for the audio streams. Best regards JC
Received on Wednesday, 19 February 2003 14:57:28 UTC